1. Technical Field
The invention relates to the heat dissipation of electronic components, particularly to fastening structures and heat dissipation of the non-insulation package components.
2. Related Art
Modern electronic components tens to high speed and/or high frequency, so there are many electronic components associated with heat dissipation units. For example, TO-220 is a common packaging specification used for transistors and silicon-controlled rectifiers (SCRs) as shown in FIG. 1. The TO-220 components are a kind of non-insulation type package component. It features a rectangular metal tab 11 protruding from the bottom of a plastic package. The metal tab 11 is provided with a through hole 111 with a diameter of about 3.6 mm for being penetrated by a fastener 2 to screw into a tapped hole 41 of the heat dissipation unit 4. In order to insulate the metal tab 11 against the heat dissipation unit 4, an insulation sheet 3 must be sandwiched therebetween. The insulation sheet 3 is provided with a via hole 31 corresponding to the through hole 111. Because the insulation sheet 3 is a sheet of soft plastic, to prevent the via hole 31 from being damaged by the fastener 2, a two-stepped washer 22 must be disposed.
The washer 22 is composed of a narrow portion 221 and a wide portion 222. The wide portion 222 is sandwiched between a head 21 of the fastener 2 and the metal tab 11. The narrow portion 221 penetrates into the through hole 111 and via hole to protect an edge of the via hole 31. However, in a production line, the metal tab 11, insulation sheet 3 and heat dissipation unit 4 are overlapped in advance to align the though hole 111 with the via hole 31 and tapped hole 41. On the other hand, the fastener 2 first penetrates the washer 22 and then penetrates the through hole 111, via hole 31 and tapped hole 41 as shown in FIG. 2. The fastener 2 tends to split or scratch the edge of the via hole 31 while it is penetrating these holes 111,31,41. The damaged via hole 31 cannot completely insulate the metal tab 11 against the heat dissipation unit 4. As a result, an electric arc may happen.